Discusses the concepts of Optical density and how it controls refraction of light. Conceptual post! Go for it.

When we mess up with the concepts of mole and molecule then this is a must read. Will help to solve related numerical problems once you get the concepts clearer,5) Centripetal ForceAn awesome posts with a list of facts and detailed step by step explanations about Centripetal force, centrifugal post and other related concepts. Must Read for students and all Physics lovers.6) Free Fall versus Fall against air Drag force, Terminal Velocity